Chemical sensitization of photographic emulsions



a e I 2,743,182 United States Patent ce CHEMICAL SENSITIZATION OF PHOTOGRAPHIC EMULSIONS Wesley G. Lowe, Jean E. Jones, and Harry E. Robert's,

Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation oE-New Jersey No Drawing. Application November 8, 1952,

Serial No. 319,616

1 Claim. (Cl. 95--7) formation of silver sulfide on the surface of the silver halide crystal or results inv the formation of small amounts of silver from the reduction of silver halide, which effect may be in addition to the former etfect sometimes known as sulfur sensitizing. The present invention is con cerned primarily with chemical sensitization apparently of the latter type.

Among the materials previously proposed for agumenting emulsion sensitivity may be mentioned basic compounds such as ammonia and certain aromatic and aliphatic amines such as triethylamine and triethanolamine; whereas other amines such as propylamylhexylamine are said to have no effect upon emulsion sensitivity. Similarly, it has been found that simple polyamines such as ethylene di-amine are not effective chemical sensitizers for silver halide emulsions. On the other hand, there have been discovered certain polyamine compounds similar in structure to ethylene diamine which are powerful sensitizers for silver halide emulsions, as disclosed in the Lowe et al. U. S. Patents 2,518,698 granted August 15, 1950, and 2,521,925 granted September 12, 1950.

it has now been found that when silver halide emul-' sions are sensitized with the combination of a sulfur sensitizing agent, a gold salt sensitizing agent and a polyamine sensitizing agent, a speed increase is obtained greater than that expected from the individual eiiects of the sensitizers and greater than that expected from the combined effects of any two of the three types of sensitizers. a

One object of our invention is to provide chemically sensitized silver halide emulsions of enhanced sensitivity.

Another object is to provide photographic emulsions having sensitivity enhanced by a combination of sulfur, gold and polyarnine sensitizing agents; A further object is to provide the methods of augmenting emulsion sensitivity utilizing the novel combination of sensitizing agents. Another object is to provide photographic elements in which the novel emulsions are useful. Further objects triethylene tetramine or tetra'ethylene pen-tamine, tetrap'ropyl-ene pen-tarni-ne, and the like. The compounds have the general structure Where n is a positive integer from one to five, preferably 7 allyl isothiocyanate, thiocarb'anilide, sodium thiosulfate,

thioacetamide and allyl thiourea.

The sensitizers are incorporated into the emulsion at any stage in their preparation but. preferably before digestion is complete. That is, the emulsion can be first sensitized with a sulfur sensitizing agent and a gold salt sensitizing agent followed by addition of a polyamine sensitizing agent or the addition of the polyamine sensitizing agent may be made prior to the addition of the gold salt sensitizing agent. However, it. is, preferred to Partially digest an emulsion in the presence of asulfur sensitizing agent and a gold salt sensitizing agent and to finish digestion after addition of one of the indicated polyamine sensitizing compounds since'the greatest speed increases are thus obtained. Also, our sensitizing agents. in combination are useful with a variety of emulsions, producing pronounced. speed increases in either negative or positive types of emulsions. 1

Our invention will now be illustrated by reference to the following specific. examples: y

Eirample I (A) To a m d um speed n ati type si er bru se iodide emulsionv ther was added. allylthioutea (20 mg..

of our invention will become apparent from consideration of the fiollowing description.

The objects of our invention are accomplished by incorporating into silver halide emulsions a mixture of (A) a polyamine compound such as spertnine which has the formula i or a pol'yarnine compound such as diethylene triamine,

P61111101 fs ver, ha i and pota si m chlorna-urat (1.75 mg. per mol of silver halide) and the emulsion was digested for 20 minutes at. C d a portion coated onto film.

To a sample lsi A was added th s y'lene. tetramine (10 mg. per mol of silver halide) and th'e emulsion was digested for 30 minutes at 40 C.

emulsion was. then coated onto a film support.

The coatings of emulsions A and B were then ex.-

posed in the Ib sensi'tometer and developedfi minutes in the Example 2 developer. The emulsion char cteristics are tabulated in the table (samples A and B).

Example 2 I digested for .61 minutes at; 62 C. -A sample .of the em-uision was coated onto film base.

(D) To a sample of emulsion C above were added 10 milligrams of T-ET per mol .ofsilver halide and the emulsion was digested for 20 minutes at 40 C. before coating Lon base.

(E) An emulsion was made. as in .D. exceptusing go milligrams .of TET per mol .of silver :halide- 'rhe coatings of emulsion G, D an E w e th n 23* posed in the lb sensitorneter and developed for 3 minutes in a developer of the following composition:

Water, about 125 F. (50 C.) ec.. 500 p-Methylaminophenol sulfate "grams.-- 2.2 Sodium sulfite, desiccated do 96.0 Hydroquinone do 8.8 Sodium carbonate, desiccated do 48.0 Potassium bromide do 5.0

Cold water to make 1.0 liter.

The characteristics of emulsions C, D and E are shown in the table following.

Example 3 (F) In a positive type of silver bromoiodide emulsion were incorporated 20 milligrams of allyl thiourea per mol of silver halide and 2 milligrams of potassium chloroaurate per mol of silver halide and the emulsion was digested for 61 minutes at 62 C. A sample of the emulsion was coated onto film base.

(G) To a sample of emulsion F above were added 40 milligrams of spermine tetrachloride and the emulsion was digested for 20 minutes at 40 C. before coating on film base.

(H) An emulsion was made as in G above except using 60 milligrams of spermine tetrachloride.

The coatings of emulsions F, G and H were exposed in the 1b sensitometer anddeveloped for 3 minutes in the developer of Example 2. The characteristics of emulsions F, G and H are shown in the table following.

Example 4 (K) A portion of the finished emulsion I was treated with 0.050 gram of TET per mol of silver halide and held for 30 minutes at 40 C. and then coated on a film. (L) A portion of the finished emulsion I was treated with 0.100 gram of TET per mol of silver halide and held for 30 minutes at 40 C. and then coated on a film. After exposure of the emulsion coatings in an Eastman Type IB Sensitometer, the samples were developed 5 minutes in a developer of the following composition:

Water liter 1 p-Methylaminophenol sulfate "grams; 0.3 Hydroquinone do 6.0 Sodium sulfite (dry) do 38.0 Sodium bisulfite do 1.2 Sodium carbonate (dry) do 19.0 Potassium bromide do 0.9 Citric acid do 0.7

The exposed and processed emulsion coatings containing the polyamine sensitiers were found to have increased in speed as shown in the table following (samples I, J, K and L).

Example 5 (M) Toa medium grain size gelatino-silver bromoiodide emulsion was added a sulfur sensitizer such as described above, and a gold salt sensitizing agent such as described above. The emulsion was then digested to optimum sensitivity and a portion coated on film.

(N) A portion of the finished emulsion M was treated with 0.010 gram of TET per mol of silver, held 30 minutes at 40 C. and coated on film.

(O) A portion of the finished emulsion Mwas treated with 0.010 gram of TET and 0.500 gram of benzotriazole 4 per mol of silver halide, held 30 minutes at C. and coated on film.

The emulsion samples M, N and 0 were exposed and developed (4 minutes) as in Example 2 and the characteristics of the coatings are tabulated in the table following (samples M, N and 0).

Example 6 (P) A fine-grained negative type gelatino-silver bro moiodide emulsion was sensitized with a sulfur sensitizcr such as described above and a gold salt sensitizing agent such as described above. The emulsion was then digested to optimum sensitivity and a sample coated on film.

(Q) A portion of the finished emulsion P was treated with 0.010 gram of TET per mol of silver halide, held at 40 C. for 30 minutes and then coated on to film.

Emulsion samples R, S and T were treated the same as emulsion sample Q except using 0.02, 0.04 and 0.06 gram of TET per mol of silver halide respectively.

The emulsion samples PT prepared above were exposed and developed (4 minutes) as in Example 2 and the sensitometric characteristics of the coatings are tabulated in the table following (samples P-T).

The quantity of the three sensitizing agents in the silver halide emulsions is not especially critical and can vary somewhat from the optimum amounts indicated in the above examples. For example, from about /5 to 5 times as much polyamine sensitizer can be used.

A useful procedure to employ in sensitizing the emulsions with the three sensitizing agents involves final digestion of the emulsions at a pH below neutrality of the order of 6.0. For example, in making the emulsion of Example 1B above, Emulsion 1A can be regulated to pH 6.0, the polyamine compound then added followed by digestion. Quite unexpectedly we are thus able to suppress fog which might be expected to arise through extended digestion.

1 Sample Seusltizer EGQHUHZ}! For:

4 Sulfur-l-gold 320 l 0.80 t 0.07 Suliur+gold+TET 500 use t n. in S gold 5.4 i 3.28 t 0.04 Sulfur+gold+TET 9.8 3 3.47 t ILLS 11.0 g 3.73! 0.0% Sullu1"-lgold.... 5.4 1 3.28 v.01 Sultur+gold+spermlne. 11.2 3.64 g 0.05 do 13.0 l 3.00 l 0.05 Su1iur+gold 37 l 2.1. 1 0.02 Sultur+gold- 54 i 2.37 (L05 -.do.... 58 g 2.57 r 0.05 do i 1.34 (Lll Sulfur-l-gold. m i 1. s 1 ms Sultur+gold+lET-.. 220 1.45 l 0.04 Suliur+gold+TET+benz0- 225 1.43 i 0.05

trlazole. l Sultur+gold 320 t 1.47 5 um old-l-TE t .30 0.?7 5 5 .52 t 0. )7 .do 500 g 1.54 l 0.1:) do 020 1 1. 43 f 0.12

When the other polyamines mentioned are employed in conjunction with sulfur and gold sensitized silver halide emulsions speed increases are obtained comparable to those shown in the above examples.

Inthe manner of the above examples, many types of silver halide emulsions may be treated with the novel combination of sulfur, gold and .polyamine sensitizing agents. The novel sensitizers may, in general, be employed in hydrophilic colloid emulsion vehicles; for example, gelatin, polyvinyl alcohol, partially hydrolyzed cellulose esters, such as cellulose acetate and copolymers of polyvinyl alcohol. The sensitizers are suitable for the well known types of silver chloride. silver bromide and silver iodide emulsions and emulsions containing mixtures of these halides, containing the usual emulsion addenda such as antifoggants, spreading agents, coupler compounds, etc Such emulsions are suitable to use in forming single as well as multilayer film useful in color photography which customarily include on a support two 6 or more emulsion layers sensitized to difierent regions silver halide sensitized with a sulfur sensitizing agent, a of the visible spectrum and may or may not contain cougold salt sensitizing agent and triethylene tetramine.

pler compounds. According to our invention such color films carry at least one emulsion layer containing the mentioned combination of sensitizing agents.

References Cited in the file of this patent UNITED STATES PATENTS Our invention having been described, we would have it understood that the preceding description is by way v f "2 i2 of example only and that our invention is to be taken 2521925 6 f 1950 as limited only by the scope of the appended claim. a ep What We claim is: 10 2,540,086 Baldslefen et a1. Feb. 6, 1951 A light-sensitive photographic emulsion comprising 2597'856 Damschroder May 1952 

